1. Field of the Invention
The invention relates to connectors for use with fiber optic cables.
2. Description of the Prior Art
The employment of fiber optic cables or light guides, also sometimes referred to as optical communication fibers, for the transmission of information-bearing light signals, is now an established art. Much development work has been devoted to the provision of practical low-loss glass materials and production techniques for producing glass fiber cables with protective outer coatings or jackets. The jacket makes them resemble ordinary metallic-core electrical cable upon superficial external inspection. Obviously, if fiber optic cables are to be used in practical signal transmission and processing systems, practical connectors for the connection and disconnection of fiber optic cables must be provided.
Before the prior art in respect to connectors, per se, is discussed, some references will be given for the benefit of the skilled reader in understanding the state of fiber optic art in general.
An article entitled "Fiber Optics" by Narinder S. Kapany, published in the SCIENTIFIC AMERICAN, Vol. 203, Pages 72-81, dated Nov. 1960, provides a useful background in respect to some theoretical and practical aspects of fiber optic transmission.
Of considerable relevance to the problem of developing practical fiber optic connectors, is the question of transfer efficiency at the connector. Various factors, including separation at the point of abutment, and lateral separation or offset, are among the factors effecting the light transfer efficiency at a connector. In this connection, attention is directed to the Bell System Technical Journal, Vol. 50, No. 10, Dec. 1971, specifically to an article by D. L. Bisbee, entitled "Measurement of Loss Due To Offset, and End Separations of Optical Fibers". Another Bell System Technical Journal article of interest appeared in Vol. 52, No. 8, Oct. 1973 and was entitled "Effect of Misalignments on Coupling Efficiency on Single-Mode Optical Fiber Butt Joints" by J. S. Cook, W. L. Mammel and R. J. Grow.
The patent literature also contains much information relative to the state of this art. For example, U.S. Pat. No. 3,624,816 describes a "Flexible Fiber Optic Conduit". The device described therein uses a plurality of light conducting fibers in a flexible cable type arrangement.
Concerning the utility of fiber optic cables and therefore the utility of connectors for such cables, various systems are described in the patent literature which employ fiber optic cables. One example of such a utilization system is described in U.S. Pat. No. 3,809,908.
Yet another patent of interest is entitled "Glass Fiber Optical Devices," U.S. Pat. No. 3,589,793. That reference relates to the fiber optic bundles and the glass fibers themselves, as well as to a method of fabrication for the fiber optic elements themselves.
A selection of U.S. patents relating more particularly to optical cable connectors includes U.S. Pat. Nos. 3,790,791; 3,734,594; 3,637,284; 3,572,891; 3,806,225; 3,758,189 and 3,508,807 are representative of the connector prior art.
The termination pin surrounding the terminal end of a fiber bundle for insertion in a connector assembly may have any of a variety of cross-sectional shapes. Co-pending U.S. Pat. application Ser. No. 514,820, filed Oct. 15, 1974, entitled "Fiber Optic Connector and Assembly Method" describes a terminating pin arrangement of hexagonal cross-section, this being a particularly efficient shape for maximizing the ratio of glass fiber surface at the fiber bundle terminal end to the voids within the perimeter of the bundle.
The terminating pin illustrated in the aforementioned U.S. Pat. application Ser. No. 514,820, is a suitable terminating pin arrangement of hexagonal cross-section at its terminal end, for use in the combination of the present invention.
Due to tolerances in prior art arrangements, the fiber optic bundle abutment at the light signal transfer point may be slightly offset in a lateral (radial) or transverse dimension, i.e., within the plane of the said abutment. This may occur even though the axial abutment is efficiently held. Moreover, in the case of a polygon terminating pin arrangement, such as the hexagon shape contemplated in the aforementioned U.S. Pat. Application Ser. No. 514,820, there is also a rotational or twist mode alignment problem. Quite obviously, the most efficient light transmission at the abutment requires accurate lateral alignment and also requires that the termination pin cross-sectional shapes coincide, i.e., corner for corner, etc.
The manner in which the present invention deals with the aforementioned problems will be evident as this description proceeds.